What is the difference between Sound Decoders?

[AGRTERP4LIFE]

I was wondering if someone could tell me what the difference was between sound decoders?  I have a Spectrum 2-8-0 and would like to change it over to DCC with sound.  The hobby shop has decoders varying from $52 to $150.  The most expensive is a Tsunami decoder.  What is the difference?

[SteamGene]

Most people think that Tsunami has the best sound quality.  The discontinued MRC may have been better in sound quality,  but it was not reliable.  I've not heard their new release.
Gene

[AGRTERP4LIFE]

Thanks Gene.

I noticed that there is a size difference in some decoders as well.  I guess this has to do with what will fit in specific locomotives or tenders?  As far as the differences between decoders, I just wanted to make sure that I was not going to miss out on specific sounds and actions available.  Do the decoders automatically associate sound with movement?  For example, does it make specific sounds when the locomotive first starts, speeds up, etc.?

[SteamGene]

Unless you have a cam, you will need to sychronize sound to motion by programming CVs.  If you check with Tony's Train Xchange you can see specific suggestions for some of the decoders. 
Gene